In order to facilitate teaching or conducting presentations, a display device such as an electronic whiteboard has been developed. While using a conventional electronic whiteboard, a user may need to be close to the electronic whiteboard when desiring to operate or explain the currently displayed image on the electronic whiteboard. However, since the electronic whiteboard is designed to let the display data be seen by a user at a certain distance away from the electronic whiteboard, ordinary display features of the display data may not be suitable for the eyes of the user who is close to the electronic whiteboard. For example, brightness of display data of the electronic whiteboard may be designed to be higher than that suitable for the user's eyes. Therefore, the user may suffer discomfort to his/her eyes caused by the display features of display data when the user is close to the electronic whiteboard.